import java.util.ArrayList;
import java.util.List;

public class F {
    public static void main(String[] args){
        List<F> ss1 = new ArrayList<>();
        ss1.add(new C());
        C c = new C();
        F f = new F();
        List<? extends F> ss = new ArrayList(){{
            add(c);
        }};

        List<? super C> ss2 = new ArrayList(){{

        }};

        ((ArrayList<F>)ss2).add(f);

        ss.get(0);

    }
    static class C extends F{

    }
}
